EP3579500B1

EP3579500B1 - A communication system for transmitting a transmission control protocol segment over a communication network using a multipath transmission control protocol, corresponding method and computer program

Info

Publication number: EP3579500B1
Application number: EP18176515.7A
Authority: EP
Inventors: Markus Amend; Eckard Bogenfeld
Original assignee: Deutsche Telekom AG
Current assignee: Deutsche Telekom AG
Priority date: 2018-06-07
Filing date: 2018-06-07
Publication date: 2021-11-17
Anticipated expiration: 2038-06-07
Also published as: ES2903241T3; EP3579500A1; US20210234794A1; CN112262552B; WO2019233946A1; US11329908B2; CN112262552A

Description

TECHNICAL FIELD

The present invention relates to the field of communication technology, in particular to scheduling of data sub-flows in a Multipath Transmission Control Protocol, MPTCP.

TECHNICAL BACKGROUND

The Multipath Transmission Control Protocol, MPTCP, is an extension to the classical Transmission Control Protocol, TCP, for simultaneous usage of several paths from a source to a destination. MPTCP can e.g. be used for robustness purposes or even for capacity aggregation. An integral part of MPTCP is the scheduler on the transmitter side, which is usually responsible to decide, for each TCP segment, which path to use.
A common scheduling approach may e.g. prioritize a path in a strict given order. Such a scheduling behavior may be appreciated in scenarios where less cost intensive paths are combined with expensive ones to save resources. The scheduler may e.g. stop using a low priority path and switch to a higher prioritized path. However, such a scheduling approach may not cover the case that multiple paths are bundled for capacity aggregation in combination with traffic prioritization.
In J. Postel, "Transmission Control Protocol", RFC no. 793, September 1981, principles of the classical Transmission Control Protocol, TCP, are described. In A. Ford et al., "TCP Extensions for Multipath Operation with Multiple Addresses", RFC no. 6824, January 2013, XP015086539, principles of the Multipath Transmission Control Protocol, MPTCP, are described, indicating that all MPTCP operations are signaled with a TCP option being a single numerical type for MPTCP, with "sub-types" for each MPTCP message, and indicating the use of the MP_PRIO option, shown in Figure 11, to change the 'B' flag of the subflow on which it is sent, from "backup" to "priority".
In US 2016/0212759 A1 , an MPTCP scheduling approach is described.
In V. Jacquot, "Test Bed for Multipath TCP" (Thesis submitted for examination for the degree of M. Sc. in Technology, May 22, 2013; pages 1-57), a packet scheduler for scheduling data packets on different data sub-flows is disclosed, wherein priorities of the data sub-flows may be considered. In this regard, two different priority levels are supported: (i) a normal priority, and (ii) a backup priority. For associating a respective priority level go a respective data sub-flow, the standardized options "MP_PRIO" or "MP_JOIN" of the MPTCP standard are used.
In US 2017/0078206 A1 , a data transmission control apparatus configured to control data transmission between two communication parties of a Multipath Transmission Control Protocol (MPTCP) connection is disclosed. At least one TCP sub-flow is selected on which data transmission control needs to be performed, and an adjustment policy for an input item of an MPTCP congestion control algorithm is determined.
In Choi Kae Won et al., "Optimal load balancing scheduler for MPTCP-based bandwidth aggregation in heterogeneous wireless environments" (Computer Communications, vol. 112, pages 116-130, November 01, 2017), a load balancing scheduler for MPTCP-based bandwidth aggregation is disclosed which is designed to overcome the problem of possible arising of degradation of the performance of MPTCP due to the head-of-line (HOL) blocking caused by path heterogeneity, when a buffer size is limited.

SUMMARY

It is an object of the invention to provide an efficient scheduling concept for a Transmission Control Protocol, TCP, segment using a Multipath Transmission Control Protocol, MPTCP.
This object is achieved by the features of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.
In the invention, a scheduler of a communication device uses at least one priority indicator indicating a respective priority of a respective data sub-flow of an MPTCP data flow, and decides, based on the at least one priority indicator, which data sub-flow to use for transmitting a TCP segment. The scheduler uses at least one latency indicator indicating a respective latency of a respective data sub-flow, and decides, based on the at least one latency indicator, which data sub-flow to use for transmitting the TCP segment. The at least one priority indicator is provided by a network entity, which determines the priorities of the data sub-flows based on cost parameters. The at least one priority indicator may, alternatively or additionally, be stored in a memory of the communication device. The at least one priority indicator serves as a primary criterion for selecting the data sub-flow; the at least one latency indicator serves as a secondary criterion for selecting the data sub-flow. If, however, there are at least two data sub-flows with the same highest priority, the scheduler selects the data sub-flow having the lowest latency within that sub-group of data sub-flows with the same priority.
According to a first aspect, the invention relates to a communication system for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP. The communication system comprises a communication device, a further communication device and a network entity. The communication device comprises a communication interface configured to establish an MPTCP data flow comprising a plurality of data sub-flows to the further communication device, wherein the plurality of data sub-flows is combined for capacity aggregation.
The communication device comprises a scheduler configured to select, for the TCP segment, a data sub-flow from the plurality of data sub-flows. The communication interface is further configured to transmit the TCP segment via the data sub-flow selected by the scheduler to the further communication device. The network entity is configured to determine, for each of the plurality of sub-flows, at least one priority indicator indicating a respective priority of a respective data sub-flow. The network entity comprises a processor configured to determine a plurality of cost parameters of the plurality of data sub-flows, wherein each cost parameter indicates a cost of a respective data sub-flow, to determine a plurality of priorities of data sub-flows based on the plurality of cost parameters, and to generate the at least one priority indicator based on the plurality of priorities. The communication interface of the communication device is configured to receive at least one priority indicator from a network entity. The at least one priority indicator indicates a respective priority of a respective data sub-flow. The scheduler is configured to determine a data sub-flow with the highest priority from the plurality of data sub-flows and, if exists, a sub-group of the plurality of data sub-flows, wherein each data sub-flow within the sub-group has the highest priority. The scheduler is configured to determine at least one latency indicator, wherein the at least one latency indicator indicates a respective latency of a respective data sub-flow. The scheduler is configured to select, for the TCP segment, the data sub-flow from the plurality of data sub-flows based on the at least one priority indicator as a primary criterion and based on the at least one latency indicator as a secondary criterion, by selecting, for the TCP segment, the data sub-flow having the highest priority, but if, however, there are at least two data sub-flows with the same highest priority, the data sub-flow having the lowest latency within the sub-group of data sub-flows with the same priority.
In an embodiment, the network entity is a dedicated server within a core network of a communication network.
In an embodiment, the scheduler is configured to determine, for the TCP segment, a respective availability status of each data sub-flow of the plurality of data sub-flows, and to discard, for the TCP segment, all non-available data sub-flows from the plurality of data sub-flows. Thus, the data sub-flow may be selected more efficiently.
In an embodiment, the scheduler is configured to determine the at least one latency indicator based on at least one TCP transmission acknowledgement, ACK, message associated with at least one previous TCP segment. Thus, the scheduler may determine the at least one latency indicator using inherent present latency information provided by the Multipath Transmission Control Protocol, MPTCP.
In an embodiment, the plurality of data sub-flows is associated with a plurality of sockets, wherein each data sub-flow is associated with a respective socket, wherein the scheduler is configured to select a socket from the plurality of sockets, wherein the selected socket is associated with the selected data sub-flow, wherein the communication interface is configured to transmit the TCP segment via the selected data sub-flow to the further communication device using the selected socket. Thus, the TCP segment can be transmitted more efficiently.
In an embodiment, the communication interface is configured to communicate via at least one data sub-flow of the plurality of data sub-flows using a first radio access technology, and to communicate via at least one data sub-flow of the plurality of data sub-flows using a second radio access technology, wherein the first radio access technology and the second radio access technology are different. Thus, a plurality of consecutive TCP segments may be transmitted using different radio access technologies; thereby increasing transmission reliability over the Multipath Transmission Control Protocol, MPTCP.
In the last embodiment, the communication interface may be configured to communicate concurrently using the first radio access technology and the second radio access technology, and/or the first radio access technology is a Wi-Fi radio access technology and the second radio access technology is a mobile, in particular a Long Term Evolution, LTE, radio access technology. A switching between the first radio access technology and the second radio access technology may be performed for each TCP segment of the plurality of consecutive TCP segments. Thus, no deactivation and/or reactivation of a respective radio access technology may be required.
Complementary radio access technologies in terms of coverage and/or data rate may be used; thereby further increasing transmission reliability over the Multipath Transmission Control Protocol, MPTCP.
According to a second aspect, the invention relates to a method for transmitting a Transmission Control Protocol, TCP, segment from a communication device comprising a communication interface and a scheduler to a further communication device over a communication network using a Multipath Transmission Control Protocol, MPTCP. The plurality of data sub-flows is combined for capacity aggregation. The method comprises establishing, by a communication interface, an MPTCP data flow comprising the plurality of data sub-flows to a further communication device. The method comprises receiving, by the communication interface, a priority indicator from a network entity, wherein the priority indicator indicates a respective priority of a respective data sub-flow and has been generated by a processor of the network entity based on a plurality of priorities of data sub-flows, based on a plurality of cost parameters of the plurality of data sub-flows and determined by the processor. The method comprises selecting, by the scheduler, for the TCP segment, a data sub-flow from the plurality of data sub-flows based on the priority indicator as a primary criterion and based on a latency indicator indicating a respective latency of a respective data sub-flow, determined by the communication interface, as a secondary criterion, by selecting, for the TCP segment, the data sub-flow having the highest priority, but if, however, there are at least two data sub-flows with the same highest priority, the data sub-flow having the lowest latency within that sub-group of data sub-flows with the same priority. The method comprises transmitting, by the communication interface, the TCP segment via the selected data sub-flow to the further communication device.
According to a third aspect, the invention relates to a computer program comprising a program code for performing the method of the second aspect.
The invention can be implemented in hardware and/or software.

BRIEF DESCRIPTION OF THE FIGURES

Implementation forms of the invention will be described with respect to the following figures, in which:

Fig. 1 shows a schematic diagram of a communication device;
Fig. 2 shows a schematic diagram of a network entity;
Fig. 3 shows a schematic diagram of a communication system;
Fig. 4 shows a schematic diagram of a method;
Fig. 5 shows a schematic diagram of a communication system;
Fig. 6 shows a schematic diagram of a switching between radio access technologies; and
Fig. 7 shows a schematic flow diagram of a scheduling to be performed by a scheduler.

DETAILED DESCRIPTION OF THE FIGURES

Fig. 1 shows a schematic diagram of a communication device 100 for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP. The communication device 100 comprises a communication interface 101 configured to establish an MPTCP data flow comprising a plurality of data sub-flows to a further communication device, and to receive at least one priority indicator from a network entity, wherein the at least one priority indicator indicates a respective priority of a respective data sub-flow. The communication device 100 may comprise a memory configured to store at least one priority indicator, wherein the at least one priority indicator indicates a respective priority of a respective data sub-flow. The at least one priority indicator received from the network entity and the at least one priority indicator stored in the memory may together provide the plurality of priorities of the plurality of data sub-flows. The communication device 100 further comprises a scheduler 103 configured to select, for the TCP segment, a data sub-flow from the plurality of data sub-flows based on the at least one priority indicator. The communication interface is configured to transmit the TCP segment via the selected data sub-flow to the further communication device.
The communication interface 100 may comprise a first sub-interface for communicating using a first radio access technology and a second sub-interface for communicating using a second radio access technology. The at least one priority indicator may be received by any one of the first sub-interface or the second sub-interface. At least one data sub-flow of the plurality of data sub-flows may be associated with the first sub-interface or first radio access technology, respectively, and at least one data sub-flow of the plurality of data sub-flows may be associated with the second sub-interface or second radio access technology, respectively. The first radio access technology may e.g. be a Wi-Fi radio access technology, and the second radio access technology may e.g. be a mobile, in particular a Long Term Evolution, LTE, radio access technology.
A respective priority of a respective data sub-flow may be associated with the type of the radio access technology. For example, the at least one data sub-flow being associated with the LTE radio access technology may have a lower priority than the at least one data sub-flow being associated with the Wi-Fi radio access technology. Such association of priorities may preferably be indicated by priority indicators stored in the memory, and may not be provided by the network entity, since it may be known that a cost parameter relating to the LTE radio access technology may in general be higher than a cost parameter relating to the Wi-Fi radio access technology.
Fig. 2 shows a schematic diagram of a network entity 200 for determining at least one priority indicator being associated with a respective data sub-flow. The network entity 200 comprises a processor 201 configured to determine a plurality of cost parameters of the plurality of data sub-flows, wherein each cost parameter indicates a cost of a respective data sub-flow, to determine a plurality of priorities of the plurality of data sub-flows based on the plurality of cost parameters, and to generate the at least one priority indicator based on the plurality of priorities. The network entity 200 further comprises a communication interface 203 configured to transmit the at least one priority indicator to a communication device. The network entity 200 may e.g. be a dedicated server, e.g. within a core network of the communication network.
Fig. 3 shows a schematic diagram of a communication system 300 for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP. The communication system 300 comprises a communication device 100 and a further communication device 301. The communication system 300 may further comprise a network entity 200.
The further communication device 301 may be an arbitrary communication device able to communicate using the Multipath Transmission Control Protocol, MPTCP. The further communication device 301 may, however, have the same functionality and/or features as the communication device 100.
The network entity 200 transmits at least one priority indicator indicating a respective priority of a respective data sub-flow to the communication device 100 and/or to the further communication device 301 over the communication network. The communication device 100 may be configured to forward the at least one priority indicator to the further communication device 301, or vice versa. Thus, the at least one priority indicator may be exchanged between the communication device 100 and the further communication device 301, in particular if a respective priority indicated by the at least one priority indicator changes. This may allow for mutual adapting the scheduling of the communication device 100 and the further communication device 301.
The communication device 100 and the further communication device 301 communicate using the Multipath Transmission Control Protocol, MPTCP. The communication device 100 receives at least one priority indicator from the network entity 200 and may use the received at least one priority indicator for scheduling or traffic distribution to the further communication device 301. The communication device 100 may forward the at least one priority indicator to the further communication device 301. The further communication device 301 may use the received at least one priority indicator for scheduling or traffic distribution to the communication device 100.
Fig. 4 shows a schematic diagram of a method 400 for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP. The method 400 comprises establishing 401, by a communication interface, an MPTCP data flow comprising a plurality of data sub-flows to a further communication device, receiving 403, by the communication interface, at least one priority indicator from a network entity, wherein the at least one priority indicator indicates a respective priority of a respective data sub-flow, selecting 405, by a scheduler, for the TCP segment, a data sub-flow from the plurality of data sub-flows based on the at least one priority indicator, and transmitting 407, by the communication interface, the TCP segment via the selected data sub-flow to the further communication device.
Fig. 5 shows a schematic diagram of a communication system 300 for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP. The communication system 300 comprises a communication device 100 with a scheduler 103 and a further communication device 301. Each data sub-flow of the plurality of data sub-flows is referred to by a respective index number 1 to n. The scheduler 103 may detect that a currently high prioritized and/or used data sub-flow becomes unavailable by losing its capability to transmit a TCP segment, and may switch to a lower prioritized data sub-flow, which has the highest priority of all remaining available data sub-flows.
Fig. 6 shows a schematic diagram of a switching between radio access technologies. At least one data sub-flow of the plurality of data sub-flows is associated with a Wi-Fi radio access technology as first radio access technology, and at least one data sub-flow of the plurality of data sub-flows is associated with a Long Term Evolution, LTE, radio access technology as a second radio access technology. An overall throughput of 70 Mbit/s shall be realized using the Wi-Fi radio access technology and the Long Term Evolution, LTE, radio access technology, wherein the Wi-Fi radio access technology has a maximum throughput of 50 Mbit/s in this example.
In a first time interval, e.g. between -55 s and -40 s, the throughput of the Wi-Fi radio access technology is over the throughput of the Long Term Evolution, LTE, radio access technology. In a second time interval, e.g. between -35 s and -25 s, the throughput of the Long Term Evolution, LTE, radio access technology is over the throughput of the Wi-Fi radio access technology. In a third time interval, e.g. between -20 s and -7.5 s, the throughput of the Wi-Fi radio access technology is over the throughput of the Long Term Evolution, LTE, radio access technology. The Wi-Fi radio access technology and the Long Term Evolution, LTE, radio access technology are used concurrently to communicate.
Consequently, several data sub-flows may be combined for capacity aggregation, wherein the prioritization may be kept active. The usage of high prioritized data sub-flows can be ensured up to the respective data rate limit or capacity limit. On top, lower prioritized data sub-flows can be used e.g. in a given order. The communication device may thus be suited for bundling multiple paths for capacity aggregation in combination with traffic prioritization.
Fig. 7 shows a schematic flow diagram of a scheduling to be performed by a scheduler. The flow diagram provides further features of the step of selecting 405 of a data sub-flow from the plurality of data sub-flows as shown in Fig. 4. Whenever the scheduler may have to take a decision, it may runs through sub-steps 701 to 713 and may return the socket (sk), which the selected data sub-flow is associated with. The selected data sub-flow has the highest priority (prio), wherein, in this example, a low numerical value is assumed to relate to a high priority within an available data sub-flow. If several data sub-flows exist with the same highest priority, the data sub-flow with the lowest latency within this sub-group is selected. In this example, the latency is represented by the round-trip-time (rtt). Other mechanisms for capacity estimation may equally be applied, as well as another handling approach if several data sub-flows have the same priority or cost.
The sub-steps 701 to 713 are performed by the scheduler for each TCP segment to be transmitted. The sub-steps 701 to 713 will be described in more detail in the following:

In sub-step 701, a counter variable "i" is initialized to "0", a socket variable ("sk") is initialized to "NULL", a minimum priority value ("minprio") is initialized to a predefined maximum value, and a minimum latency value ("minrtt") is initialized to a predefined maximum value.
In sub-step 703, the current counter variable "i" is compared with the number of data sub-flows ("#subflows"). If the current counter variable "i" is smaller than the number of data sub-flows ("#subflows"), the procedure proceeds with sub-step 705; otherwise with sub-step 713.
In sub-step 705, it is verified whether the current data sub-flow indexed by the counter variable "i" ("subflow[i]") is available, e.g. able to transmit data. If the current data sub-flow indexed by the counter variable "i" ("subflow[i]") is available, the procedure proceeds with sub-step 707; otherwise with sub-step 711.
In sub-step 707, it is verified whether the priority of the current data sub-flow ("prio(subflow)") is smaller than the current minimum priority value ("minprio"). Furthermore, if the priority of the current data sub-flow ("prio(subflow)") is equal to the current minimum priority value ("minprio"), it is verified whether the latency of the current data sub-flow ("rtt(subflow)") is smaller than the current minimum latency value ("minrtt"). If any of these two alternatives applies, the procedure proceeds with sub-step 709; otherwise with sub-step 711.
In sub-step 709, the minimum priority value ("minprio") is updated to the priority of the current data sub-flow. Furthermore, the minimum latency value ("minrtt") is updated to the latency of the current data sub-flow. Moreover, the socket variable ("sk") is updated such as to correspond to the current data sub-flow. The procedure proceeds with sub-step 711.
In sub-step 711, the counter variable "i" is incremented by "1" ("i++"). The procedure proceeds with sub-step 703. By incrementing the counter variable "i" and proceeding with sub-step 703, and repeating the procedure, a searching loop is realized, which searches for the data sub-flow having the highest priority as a primary criterion and the lowest latency as a secondary criterion. If all data sub-flows have been searched, the search loop terminates and proceeds with sub-step 713.
In sub-step 713, the socket variable ("sk") corresponding to the socket of the selected data sub-flow is returned.
In summary, a path prioritization scheduling decision based on external and inherent information associated with the data sub-flows can be realized. The priorities may be provided using at least one priority indicator. The latencies may be provided using at least one latency indicator, wherein TCP transmission acknowledgement, ACK, messages may be exploited for determining the respective latencies.

REFERENCE SIGNS

100: Communication device
101: Communication interface
103: Scheduler

200: Network entity
201: Processor
203: Communication interface

300: Communication system
301: Further communication device

400: Method
401: Establishing
403: Receiving
405: Selecting
407: Transmitting

701: Sub-step
703: Sub-step
705: Sub-step
707: Sub-step
709: Sub-step
711: Sub-step
713: Sub-step

Claims

A communication system (300) for transmitting a Transmission Control Protocol, TCP, segment over a communication network using a Multipath Transmission Control Protocol, MPTCP, the communication system (300) comprising a communication device (100), a further communication device (301) and a network entity (200), wherein
the communication device (100) comprises:
- a communication interface (101) configured to establish an MPTCP data flow comprising a plurality of data sub-flows to the further communication device (301), wherein the plurality of data sub-flows is combined for capacity aggregation, and

- a scheduler (103) configured to select, for the TCP segment, a data sub-flow from the plurality of data sub-flows, wherein the communication interface (101) is further configured to transmit the TCP segment via the data sub-flow selected by the scheduler (103) to the further communication device (301), the network entity (200) is configured to determine, for each of the plurality of sub-flows, at least one priority indicator indicating a respective priority of a respective data sub-flow,
the network entity comprises:
- a processor (201) configured to determine a plurality of cost parameters of the plurality of data sub-flows, wherein each cost parameter indicates a cost of a respective data sub-flow, to determine a plurality of priorities of the plurality of data sub-flows based on the plurality of cost parameters, and to generate the at least one priority indicator based on the plurality of priorities, and

- a communication interface (203) configured to transmit the at least one priority indicator for a respective sub-flow to the communication device (100),
wherein:
a.) the communication interface (101) of the communication device (100) is configured to receive at least one priority indicator from a network entity (200), wherein the at least one priority indicator indicates a respective priority of a respective data sub-flow,

b.) the scheduler (103) of the communication device (100) is configured to determine a data sub-flow with the highest priority from the plurality of data sub-flows and, if exists, a sub-group of the plurality of data sub-flows, wherein each data sub-flow within the sub-group has the highest priority,

c.) the scheduler (103) of the communication device (100) is configured to determine at least one latency indicator indicating a respective latency of a respective data sub-flow, and

d.) the scheduler (103) of the communication device (100) is further configured to select the data sub-flow for the TCP segment from the plurality of data sub-flows, based on the at least one priority indicator as a primary criterion and based on the at least one latency indicator as a secondary criterion, by selecting, for the TCP segment, the data sub-flow having the highest priority, but if, however, there are at least two data sub-flows with the same highest priority, the data sub-flow having the lowest latency within that sub-group of data sub-flows with the same priority.
The communication system (300) of claim 1, wherein the network entity (200) is a dedicated server within a core network of the communication network.
The communication system (300) of claim 1 or 2, wherein the scheduler (103) of the communication device (100) is configured to determine, for the TCP segment, a respective availability status of each data sub-flow of the plurality of data sub-flows, and to discard, for the TCP segment, all non-available data sub-flows from the plurality of data sub-flows.
The communication system (300) of any one of the preceding claims, wherein the scheduler (103) of the communication device (100) is configured to determine the at least one latency indicator based on at least one TCP transmission acknowledgement, ACK, message associated with at least one previous TCP segment.
The communication system (300) of any one of the preceding claims, with the communication device (100), wherein the plurality of data sub-flows is associated with a plurality of sockets, wherein each data sub-flow is associated with a respective socket, wherein the scheduler (103) is configured to select a socket from the plurality of sockets, wherein the selected socket is associated with the selected data sub-flow, wherein the communication interface (101) is configured to transmit the TCP segment via the selected data sub-flow to the further communication device (301) using the selected socket.
The communication system (300) of any one of the preceding claims, wherein the communication interface (101) of the communication device (100) is configured to communicate via at least one data sub-flow of the plurality of data sub-flows using a first radio access technology, and to communicate via at least one data sub-flow of the plurality of data sub-flows using a second radio access technology, wherein the first radio access technology and the second radio access technology are different.
The communication system (300) of claim 6, wherein the communication interface (101) of the communication device (100) is configured to communicate concurrently using the first radio access technology and the second radio access technology.
The communication system (300) of any one of claims 6 or 7, wherein the first radio access technology is a Wi-Fi radio access technology, and wherein the second radio access technology is a mobile, in particular a Long Term Evolution, LTE, radio access technology.
A method (400) for transmitting a Transmission Control Protocol, TCP, segment from a communication device (100) comprising a communication interface (101) and a scheduler (103) to a further communication device (301) over a communication network using a Multipath Transmission Control Protocol, MPTCP, wherein a plurality of data sub-flows is combined for capacity aggregation,
wherein the method (400) comprises:
establishing (401), by the communication interface (101) of the communication device (100), an MPTCP data flow comprising the plurality of data sub-flows to the further communication device (301);

receiving (403), by the communication interface (101), a priority indicator from a network entity (200), wherein the priority indicator indicates a respective priority of a respective data sub-flow and has been generated by a processor (201) of the network entity (200) based on a plurality of priorities of the plurality of data sub-flows, based on a plurality of cost parameters of the plurality of data sub-flows as determined by the processor (201);

selecting (405 [701, 703, 705, 707, 709, 711]), by the scheduler (103), for the TCP segment, a data sub-flow from the plurality of data sub-flows based on the priority indicator as a primary criterion and based on a latency indicator indicating a latency of a respective sub-flow and determined by the communication interface (101), as a secondary criterion, by selecting, for the TCP segment, the data sub-flow having the highest priority, but if, however, there are at least two data sub-flows with the same highest priority, the data sub-flow having the lowest latency within that sub-group of data sub-flows with the same priority; and

transmitting (407), by the communication interface (101), the TCP segment via the selected data sub-flow to the further communication device (301).
A computer program comprising a program code for performing the method (400) of claim 9.